The preparation of relatively pure samples of nucleic acids such as DNA or RNA is an important step in many molecular biology procedures. Purification is necessary to ensure removal of impurities, e.g., cellular debris, that may interfere with subsequent molecular biological procedures. RNA purification has many uses such as in the preparation of cDNA and the monitoring of gene expression. While the purification of DNA from many types of cells is relatively straight forward, RNA purification is often problematic. Such difficulties include the need to inactivate ubiquitous RNA degrading enzymes and the lability of RNA in alkaline pH environments. Another difficulty with RNA purification is the frequent co-purification of RNA and DNA. Contaminating DNA may interfere with subsequent molecular biochemical or genetic analysis procedures because of the similar base pairing properties of DNA and RNA. Similarly, RNA may contaminate DNA preparations.
Numerous procedures have been developed for purifying RNA. These previously available RNA procedures suffer from one or more shortcomings such as the need for highly toxic chemicals, the use of an inconveniently large number of manipulations, genomic DNA contamination, a requirement for ultracentrifugation, the use of DNAses, RNAses, proteinase digestions, and contamination with inhibitors of genetic analysis procedures (e.g., PCR and base sequencing). Such RNA isolation methods usually include the cumbersome steps of adsorbing nucleic acids to a solid phase support and subsequently preferentially eluting the nucleic acid from the supports. Similar problems arise with previously available techniques for DNA isolation. Accordingly, it is of interest to provide new and improved methods of RNA and DNA purification. Ideally, such new methods are simple to perform and may easily be automated.